Settling of phosphate ore materials



SETTLING 0F PHOSPHATE OBE MATERIALS Filed oct. 15, 1942 v .4 Sheets-Sheet l 0 F. 0 f m N 0 TKEHTEB 0 I Z 3 4 5 6 7 8 910 Il 1215141516 TRL-MED UNT/M4750 m mum.

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may s. mel/4J wfn C /x/M Patented Aug. 7, 1945k SETTLING F PHOSl-HATE ORE MATERIALS Donald S. Phelps, Harvard, Mass., assignor to The American Agricultural Chemical Company, New York, N. Y., a corporation of Delaware Application October 13, 1942, Serial No. 461,886

,7 Claims.

The present invention relates to a fundamental l discovery which I have made in the art of phosphate mining and recovery, namely, that a certain class of chemical reagents, which, for convenience, I have designated as phosphateore sedimentation-acceleration reagen or settling-acceleration reagents, as I sometimes call them, and which are hereafter described, de-

lined and illustrated, have the remarkable property of producing a greatly accelerated rate bi sedimentation or settling of aqueous suspensions,

pulps or slurries of phosphate ores, when the reagents are added thereto in relatively small and economical quantities, and, generally, but not always necessarily, in an alkaline state, or with, or in the presence of, an alkaline reagent.

. The invention relates specically to .the treatment of phosphate ores; and, in particular, to a process for .treatment and recovery `of such ores wherein an aqueous suspension, pulp or slurry of lthe ore, or part of it, more especially the finer particles thereof (many of which are too fine to settle rapidly even instill water) is subjected .to accelerated sedimentation by treatment with one or more of my novel "sedimentation-acceleration reagents of the class referred to, and the thus-settled material is then recovered or co1- lected, and then subjected to various separation treatments for separation and concentration of valuable phosphate materials, including those which would otherwise go t0 waste, or which could not be recovered for along time.

Objects of the invention include attainment of the results just stated'.

Inthe usual hydraulic process of mining phosphate ore, more especially Florida pebble phosphate, which'does not require crushing or grinding, the overburden of earth is ilrst removed and the exposed banks of phosphate ore (containingV the phosphate mineral or. phosphate rock) are then hydraulically mined, by means of streams of water under high pressure. The resulting slurry is then pumped to a phosphate washer or recovery plant, often known generically in the industry, as a "wa'sher, and sometimes so referred to in the following description. This washer usually includes a washing, screening and hy.- draulic-separation or classification installation,

followed by tabling, dotation, sometimes electro ystatic separation, andperhaps other concentrathan 0.0011 inch in diameter, and much of it is so small that it will settle only very slowly, or not at all, from an aqueous suspension. The

feed to the washer also usually contains a cer-v tain amount of sand or quartz, clay, and perhaps other impurities and waste material. At the washer, the feed isordinarily agitated, washed, screened, hydraulically classified, and the smaller sizes of phosphate mineral, say less than about 4` mesh, are then, in many plants, concentrated from the impurities and waste by flotation, vsome- Y20 times preceded by tabling and other separation I processes.

Another method of phosphate mining, sometimes employed on domestic ores, including Florida deposits, is the so-called dry-mining process, according .to which .the phosphate-bearing sometimes electrostatic separation-the several different methods being used sometimes separately in different parts of the plant, and sometimes together, either in succession or in combination.

During all .these operations, 'the nner sizes of' I Uphosphate mineral, usually. less than approximately mesh, and sometimes considerably coarser,` and almost always-the material finer than mesh, vtend to remain suspended inthe water, together also with the finer particles of silica, sand, clay or other impurities present. I'his is especially so in the overilow product from the settling tanks, and particularly when the ow of water through such tanks is relatively rapid.

Because of economic factors, the tanks are necessarily relatively small compared to .the total volume of water. Therefore, there is usually avrapid `the washen or somevpart of the plant,

ilow through them, giving a relatively short time for settling. In some installations this time may or settling pond, some of the material may bel pumped back out of the pond and returned to for retreatment and concentration. l

Even when such re-treatment of the debris is ultimately possible, the delays are great and the phosphate` losses are high. Also, repumping the material may tend to put the fine particles back in suspension. In addition, the expense of pumping the washer or settling-tank overflow product rst' to the debris dumps or settling ponds, and later back for re-treatment, is considerable, because of the power and labor required, and there is a longl delay while natural settling takesv place.

For a period of many years this problem has been a fundamental, and perhaps" the principal, one among those engaging the attention of phosphate producers; and because the field is highly competitive and costs are extremely important,

long and repeated efforts, by many leading engineers in the iield, have been made, to find some practical solution for ,the problem of improving the recovery of this unsettled fine phosphatematerial, and to overcome the necessity for repumping and re-treating the debris.

My present discovery includes the fact that by a relatively simple and economical treatment withone or more of the phosphate ore sedimentation-acceleration reagents previously referred to, and which are hereafter described and illustrated -in detailwhich treatment is applicable, if desired, either to the initial feed from the mine to the entire "washer (i. e., to the phosphate ore .treating plant as a whole), or to other appropriate stages of the process, but which I have found preferable when applied directly in the settling tanks, or in the feed thereto-it is possible to treat the suspended material, including the phosphate mineral and impurities alike, in

such a way that its settling is greatly accelerated, and the recovery of both `the settled phosphate mineral and the impurities is greatly improved; after which the thus-settled material may'be concentrated and the desired phosphate recovered.

Mynvel treatment has been found to increase the total recovery of solids in the settling'tanks, especially when the reagent is added at that point in the process, and the treatment may be carried out to such an extent as to cbviate thenecessity of re-pumping and re-treating the debris from the debris dumps or settling ponds. It may thus result in very substantial savings, both in the recovery of phosphate (i. e; phosphate mineral) ample of the arrangement of what may be regarded as a typical phosphate washer in the case of an hydraulic mining operation for unground Florida pebble phosphate, upon which my treatment has been found especially effective, the feed,

as pumped from the mine, passes iirst through a hammer mill (i. e., a beater type of mill), which disintegrates' the mud balls, thence by flumes to a sump. The pulp is then pumped to a set of dewatering screens and the water, containing all of the vsolids finer than approximately fourteen mesh, then goes to the sedimentation tanks and thence to the concentration plant., 'I'he oversize or plus I4 mesh goes to several sets of screens and scrubbers which wash and separate the ner particles stuck to the oversize particles, so that much of what was originally oversize eventually goes back to the sump and, if it has been further disintegrated in the meantime, has a second opportunity of becoming part of the undersize of the head screens. In this way the ore masses of phosphate mineral, clay, sand, and all other impurities become well disintegrated and particularly all the fine particles eventually reach the settling or sedimentation tanks.

The minus fourteen mesh material which eventually reaches the sedimentation tanks is there oifered a brief opportunity to settle and that portion which does settle forms the feed to the concentration plant proper. The overflow or effluent of the sedimentation tanks, containing all the particles which do not settle while in the sedimentation tanks, including' phosphate rock, clay, silica and other` impurities, goes from the settling tanks to the settling area or ponds, *which is a very large ground area dammed off for the express purpose of settling the solids, from the Water. This area may be very extensive, for example, a matter of one mile square or even more.

The flow through the settling tanks is necessarily relatively rapid, as already indicated, since it is impractical, economically, to have the tanks large enough, and to allow the liquid to remain in them for a sufilcient time, to make a full natural separation or settlement ofthe solids. The latter usually occurs only over a period of months or years, in the settling ponds; while the time allowed for settling in the sedimentation tanks may be a matter of minutes, or even, perhaps, of seconds in some cases. For example, in one illustrative installation, the time of flow across the surface was found to be between a maximum of about 30 seconds down to a minimum of about 5 seconds; while even in a very large settling tank of modern design, the time available for settling may be only of the order of about one to two minutes, or less, with an average of about, 30 seconds under certain conditions.l Thus, in the absence of treatment to produce accelerated settling, the overflow product from the settling tanks usually consists of a muddy liquid in the form of a pulp, suspension or slurry, whichV may still contain a very substantial quantity of valuable phosphate mineral, mixed with silica and other impurities, but which heretofore, it has been impossible to settle and concentrate economically, or in any practical manner, either in the settling tanks or and in the cost of the process, including a saving of power in re-pumping the debris, of labor costs, andinpreventing delay. Figures 1 and 12 hereof, more particularly described hereafter, are illustrative examples of results obtained by various treatments according to my invention. By way of an illustrative exin any other part of the plant. Not only was it impossible to separate the unsettled solids, efflciently, for any sort of subsequent treatment, but particularly by reason of the necessary hydraulic mining or washing or soaking operations, the settling tank overflow, and indeed the feed to the settling tanks as well, have been too dilute for emcient wet concentration, as by flotation, ta-

is shown by analysis of the material before setbling, and so forth. A sample of this pulp (overflow product from the settling tanks), allowed to stand quietly in a tall graduate, is usually found to settle very slowly, and sometimes not perceptibly within a short period of observation.

vA feature of the present invention resides in the discovery that by the addition of .a relatively small and economical quantity of one or more of my newly discovered phosphate ore sedimentation acceleration (settling acceleration") reagents. either directly to the settling tanks, or to the feed thereto (although it may be done at other suitable stages of the process), the settling of this hner material, including phosphate mineral and impurities alike, can be very greatly accelerated, so'that the subsequent concentration and over-al1 recovery, after settling, is much improved, even when the time in the settling tanks 'is only of the order of thosestated above. Thus the importance of a high initial settling rate will be seen, so that the amount of solids settled out .y will be high during the initial period of settling.

Addition of the reagent or reagents may be in the presence of, or accompanied by, an alkaline reagent such as caustic soda, or may be made to the pulp or suspension when in an alkaline condition. I

My novel phosphate ore sedimentation-acceleration reagents are characterized and may be distinguished by being water miscible (which term, as used herein, includes both soluble and suspensible), and by having a common action, of the character already stated, upon phosphate ore pulps, aqueous suspensions or slurries. That is to say, when the reagent is applied, -in relatively small, and economical, quantity, to an aqueous suspension of phosphate ore which is composed of, or includes, particles of both phosphate mineral and intermixed impurities, which are either too ilne to settle rapidly in flowing, or even in stili water, or will not settle at all under such circumstances, the reagent produces a markedly accelerated settling-in somecases aJ settling where none would otherwise occur, or at least, be observable, within any reasonable timeand generally oi the 'phosphate particles and impurities alike. This may produce a very substantial amount of settling within the first minute or two minutes of settling time elapsing after treatment. even where no such settling would otherwise occur; and in many instances there may be a substantial initial settling during the first 30 seconds available for settling, elapsing after `treatment with the reagent. Even when the retime and of the settled product collected after treatment. In general, these. are found to have much lthe same percentage composition, indienting that the vaccelerated settling treatment does not produce a separation of the phosphate mineral from the silica and other impurities, but causes a more rapid settling of both alike.

This common action upon phosphate ore suspensions is a striking common characteristic of my novel class of materials, and is an important feature by which they can be determined and recognized,

Another means of identification of my novel class of reagents is that all of them, so far as I know, are, and many of them are known to be, deocculating or dispersin'g agents for various materials. Many of them have been suggested or used for various separating, deilocculating, dispersion or flotation applications, as regards a variety of materials and ores, some of them for phosphate materials; but the mere fact that the material is so known as a deocculating or dispersing agent, for another ore oreven for phosphate, is not, s0 far as I am at present aware, a suicient criterion to determine or predict with certainty, whether it falls within lthe present class of phosphate ore settling-acceleration reagents. That is to say, thev possessionuof deocculating or dispersing properties is, as at present advised, a necessary but vnot a self-sufficient condition for successful use in my process.

According to my best present information, certain deocculating or dispersing agents, previously known or suggested for that purpose in connection with various ores, do not possess, to any substantial degree, the property of producing accelerated settling of phosphate ores; and hence are not within the class of materials which I have discovered,.and claim herein. Examples of :such yreagents are: agar agar, gum acacia and blackstrap molasses, al1 of which have long been known as deiiocculating or dispersing agents for various ores, but which do not possess, to any subtantial degree, the property of producing accelerated settling of phosphate ores.

within my novel class of reagents, is that the ma-A terial must be one which is water-miscible (which settling tanks, its effect persists so that rapid settling occurs as soon as opportunity is presented. In other cases, it is to -be observed that my reagents, when applied in the amounts and concentrations indicated by the examples given below, have the elIect of more than doubling the volume of settled material, as compared with material not so treated with the reagents, at all times throughout a short initial settling period such as already indicated-and even in some cases given; the increase of the rate of settling being of the intermixed fine particles of both phosphate and impurities, as compared with their untreated settling rate.

In general, the action of my novel reagents lis notnne of separation or selection, but is a more rapid' settling of all the materials substantially likfe, including .b oth phosphate impurities, BS

term, as used herein, includes both soluble and suspensible) and which, whenso mixed, whether such mixture be by suspension or solution, is capable of dispersing, in water, one or more colloidal constituents of phosphate ore, in the presence of insoluble calcium phosphate. So far as at present advised, that test is a definite means of identification of my novel class of compounds.

Preferably, too, but not necessarily, the reagent is either itself alkaline in reaction, or possesses the foregoing property when in an alkaline sointion, suspension or medium; as in the presence of an alkaline reagent.

So far as I am at present aware, their common action upon phosphate ore suspensions, as

already described, and the other criteria given trat'ive, but not exclusive, examples of my novel class of materials, the following are given, and

me for the purpose. They are, in general, either themselves alkalis or are preferably employed t advantage in an alkaline state or condition, or in the presence of, or simultaneously with, an alkaline reagent, such as,v for example, caustic soda, either added separately or included with the reagent. The illustrative examples of suitable reagents follow:

(1) Sodium silicate (Na'aSiOa) and preferably having a composition of approximately.

and preferably added in an alkaline state, or together .with caustic soda, and suitably in the ,proportions of sodium silicate and caustic soda hereafter further illustrated.

(2) Molecularly dehydrated alkali phosphates, including, specifically, tetra-sodium pyrophosphate (NalPzO'z) dissolved or in solid state, and sodium metaphosphate (NaPoe).

(3) Lignin sulfate, lignin sulfonate and lignin sulte products, including wood pulp waste liquors; specically the trade-marked products known as Daxad No. 11 and Daxad No. 23, sold by Dewey & Almy Chemical Company of Cambridge, Massachusetts; Black Liquor; Goulac and Glutrin, trade-marked products sold by Robeson Process Q0., of New York.

Of the foregoing materials, my best present information is that Daxad No. 11 and Daxad No. 23 are both lignin sulfonate products; Black Liquor, as sold by the West Virginia Pulp and Paper Co., of New York, is a by-product of the paperindusltryy generally made from pine wood and containing a lignin sulfate. Goulac is a lignin sulte product derived from wood pulp waste liquor as'sold by the Robeson Process Co., of New York. This is sold in the form of a solid. Glutrin is a lignin suliite derived from wood pulp waste liquor and also sold by the Robeson Process Co., of New York. This is sold in the form of a liquid of 50% strength.

(4) 'Iri-sodium phosphate, or any sodium orthophosphate in the presence of a sumcient quantity of an alkaline reagent (e. g., caustic soda) to eiect conversion to tri-sodium yphosphate.

5) In the case of certain phosphate ores, apparently those taken from particular localities, (e. g. ore mined in the neighborhood of Hopewell, Florida (I have also found that caustic soda when used alone, for example in the proportions of about 0.5 pound or 1.0 pound of caustic soda per ton of feed, produces advantageous results, and

may, in some cases, produce results comparable with those obtained with th'e other reagents named above. This is not true,v however, of all ores; and I have not ascertained the reason for the eilectiveness of caustic soda alone in certain cases. It appears, however, to be due to some difference inthe composition of the ore, the exact nature of which Iam at present unable to explain.

'Ihe effect upon various samples of commercial grades of phosphate or pulps or suspensions,'of accelerated settling treatment with certain of the foregoing sedimentation-acceleration reagents, is illustrated in the accompanying drawings, it being understood that different results may be obtained upon different samples of ore from the same locality, or upon ore from different localities, or upon samples of different ages, or which have stood for varying periods. 'I'he foregoing and many other factors may affect thercsult;`

lthese include the best materials now known to hence the accompanying curves are illustrative only:

In making all these curves a sample of the pulp was placed in a 1000 cc. graduate and the measured amount of reagent and caustic added. 'I'he mixture was agitated and then allowed to stand. On standing `quietly small particles of phosphate and impurities settle, although the supernatant water remains turbid. The body of solids settled in the liquid at and near the bottom of the graduate can be readily seen, and

generally exhibits a reasonably denite line (ac- The pulps employed Vtorthese tests were de- A rived from commercial phosphate washer or treating plants, and are believed to be representative of a number of types of pulp or suspended ore that may be found in such plants; for variety, some pulp (as for the Fig. 1 test) was taken from the overflow or waste" of previous sedimentation tanks (which did not embody my process) and some (for the Fig. 7 and 8 tests) was derived by repulsing, in a manner that is commercially required for removal and handling, the material from lphosphate debris banks produced by the large or waste settling ponds mentioned hereinabove. v

Figure 1 is an illustrative accelerated-sedimentation curve illustrating the efIect of treatment or a one-liter sample of an aqueous phosphate suspension taken from the overflow product from a settling tank, with a settling acceleration reagent consisting of 5 cc. of a 5% solution of caustic soda and 30 cc. of a 5% solution of sodium silicate (NazSiOs), equivalenty to 1.4 pounds of caustic soda and 8.8 pounds of sodium silicate per ton oi solids in the sample pulp (suspension) under test.

In the curve marked treated, the effect of this treatment is shown, as contrasted with the effect produced by natural settling when no reagent was added to a similar sample of the same suspension. marked untreated Figure 2 is a similar illustrative curve showing the effect of treatment with caustic soda and sodium silicate. In this particular sample the total solids amount to 200 grams in a volume of feed pulp amounting to 1000 cc. The reagents were employed-in the proportion of 1.0 pound of caustic soda and 2.0 pounds of sodium silicate 40 B. per ton of solids in the feed pulp.

Figure 3 is also illustrative of the results produced upon a dierent sample by treatment with caustic-soda and sodium silicate. In this instance the treatment was with 2.0 pounds of caustic soda ing the results of treatment with caustic soda alone, for the reason that it appears to be effective only inthe case oi' particular ores, or ore taken from particular localities, I have neverphosphate (NaPQxil particular example theless obtained good results in certain instances,

upon. ore from the Hopewell (Florida) district.V

Upon certain samples of Hopewell ore I obtained results roughly comparable with those illustrated in'Flgure 2, by treatment of a sample comprising 200 grams of solids in a 1000 cc. volume of pulp with'a caustic soda solution equivalent to 1.0 pound of caustic soda'. per tonof solids in the pulp feed; and on another. sample of such ore, containing 210.grams of solid in a 1000 cc.A

volume of pulp, I obtained good results by treat- .ment with caustic soda equivalent to 0.5 pound tetra-sodium pyrophosphate (NaAPzO'z) in the proportion of 75 cc. of the solution to 500 grams of solids. The pulp had a specific gravity of 1.308 with a quantity of solids in the pulp amounting to 38.3% by weight. In this particular test the volume of the settled solids amounted to about 326 cc. per liter after 16 minutes settling time. andthe settling-acceleration reagent was employed in the proportion of 15.0 pounds of,`

reagent per ton of solids in the pulp being treated. From these illustrative curves it may be noted thati on the particular sample of phosphate material tested, there was a very rapid settling during the iirsi;y two or three minutes of settling time, when the settling-acceleration reagent was first added. This is of importance in carrying out a commercial process, because it is ordinarily possible to retain the suspension in the settling tanks, for example, for only a very brief period of settling; often less, even, than three minutes,

and very generally less than 8 to 10 minutes; and

Specific gravity of pulp 1.308 Percent solids in the pulp 38.3 Weight of solids grarns 500 The reagent used was 5 grams of dry solidA tetra-sodium pyrophosphate per liter of pulp,

equivalent to 20 pounds of the reagent per ton of solids in the pulp.

In the case of this particular sample under treatment, it is to be noted that while the untreated material was not observed to settle at all, within the period of time covered by the observations, there was a very rapid settling of thev treated material within the first three minutes. In addition to the advantages pointed out in connection with Figure 4 above, there was thus, in this' case, avery material increase in the' total volume of settled material recovered. 'I'his 'is of importance in cases where a maximum recovery is necessary. Although that can seldom be obtained economically in plant practice under present'economic conditions, it may be of extreme importance wherever supplies or natural resources are limited, e. g., under war conditions.

Figure 6 comprises similar illustrative settling curves obtained by the use of dry metathe conditions werelds follows:

specmc gravity.ofrpu1p 1.223

Percent solids in the pulp' 30.2 4 Weight of solids grams-- 371 The reagent used was 0.5 gram of dry, solid sodium metaphosphate per liter of pulp, equivalent to approximately 2.70 pounds of reagent per ton of solids in the pulp. In this case, no alkaline reagent was used, and the sodium metaphosphate employed was not alkaline in reaction when dissolved in water.v

It will be seen that, on the particular sample tested, thereagent had the advantage of producing a very rapid settling within the ilrst minute;

and also that it produced a substantial recovery of the solid material when treated, although the untreated pulp, in this instance, showed no observable settling within the period of observation.

In Figure 7 there are shown illustrative examples of curves of sedimentation, for the normal (i. e., untreated) material in the case of a pulp having a specic gravity of 1.220, with a percent of solids in the pulp amounting to 29.3%,A the weight of the dry solids amounting to 357 grams per liter; and for the same material when treated v with a, settling-acceleration reagent comprising Daxad No. 1l, in the proportion of approximately seven pounds of reagent per ton of solids in the pulp being treated,` and with caustic soda solution in the proportion of about 2.80 pounds of dry caustic soda per ton of solids in the pulp. The pulp used for this test (Fig. 7) consistedof a suspension ofA phosphate debris i. e. a mixture of phosphate mineral and impurities, which was taken from the phosphate debris dumps inen-l tioned hereinabove; the pulp having characteristics representative of the result of operations such as are necessary for repulping andA handling such debris.

In this case, also, it is to be noted that there was a marked increase in the volume of sediment obtained in the first one or two minutes of settling time when the settling acceleration reagent was used, and that there was a materiai'increase in the total volume of sediment recovered.

Figure 8 shows similar illustrative curves, illustrating the results obtained by use of Daxad No. 23. In this case a debris pulp like that used for Fig. 7 was employed, and the data were:

Specific gravity of pulp 1.220 Percent solids in pulp 29.3 Weight of solids -grams-- 357 Pounds of dry caustic soda per ton of solids 2.80

Pounds of Daxad No. 23 per ton of solids 5.60

Figure 9 comprises similar illustrative curves obtained by the use of black liquor. In this example, the conditions were as follows'.

Specific gravity of pulp 1 .220 Percent solids in pulp 29.3 Weight of solids grams 357 Pounds of dry caustic soda per ton of solids 2.80 Pounds of black liquor per ton of solids 8.14

l0.6 gram of caustic soda.

Figure 11 is a similar set of comparative curves in the case of treatment with Glutrin and caustic soda; 1000-cc. o! the pulp contained 371 grams oi'V gram of caustic soda.

In Figure 12 there are shown illustrative examples of curves of sedimentation, for the normal (i. e., untreated) material and for the treated material in the case of treatment with tri-sodium phosphate in the presence of caustic soda. The pulp under test had 'a specic gravity of 1.238

' with a percent of solids in the pulp amounting to l0 31.2% by weight. In this particular case the weight of the solids amounts to 376 grams per liter and the tri-sodium phosphate was employed in the proportion of about 26.60 pounds of tri-sodium phosphate (NaaPO-i) 4per ton solids in the pulp, 15

and with caustic soda solution in the proportion of 2.66 pounds of dry caustic soda per ton of solids in the pulp.

Tests have revealed that in operations of the sort exemplified by all of the foregoing examples,

the composition of the settled material (after drying) is approximately 35% BPLibone phosphate of lime), and that in general, the settled and dried material will all pass a 10 mesh screen, while about 945% of it is retained on a 325 mesh screen.

For convenience of reference and comparison, I- have summarized the data of the tests in the form of a composite table.

change in the composition of the settled material, as between phosphate and impurities. The material thus recovered by settling may be thereafter subjected to hydraulic classication, tabling, flotation, or any other appropriate process for concentration and recovery of the desired phosphate material.

From an examination of the foregoing illustrative curves it will be observed (for example see Figure 1) that it is a property of many of my novel reagents that when they are applied to a suspension of finely divided particles of both phosphate and impurities, even when the particles are too ne to settle rapidly from lsuch an an aqueous suspension, the appropriate amounts and concentrations of the settling acceleration reagents, as illustrated above, are suiiicient in amount and concentration to more than double the volume of settled material, as compared with material not so treated, at all times throughout an initial short period-for example, the iirst three minutes--of settling time (compare Figure l). and sometimes throughout even longer periods as shown by the other examples, such increase of the rate of settling being of the intermixed ne particles of both phosphate mineral and impurities, as compared with their untreated settling rate.

Tests with settling-acceleration reagents, on Florida phosphate ore pulpe Volume of settled product Reagent Caustic, lbs/t0n ibs/mn Pent' specic Gfms After 1 min. After 2 min. After 3 min. aan T t R t i rd f d solids in gravity solids es gage S insgds omsieeds reed offesa in feed v 136g?,-

` pulp pulp pulp l pulp pulp 2 Nat- Ac- Nat- Ac- N at- Ac- A ural, celer ural, celer., ural, ccler.,

cc. cc. cc. cc. cc. cc.

Sodium silicate 8.8 1. 4 35. 7 (l. 275) (450) 13 90 30 100 40 105 o5. 7 Soilumlsilcate 2.0 1.0 20.0 (1.110) 200 None 90 None 110 None 116 83.0

. SO li. 4.0 2. 0 25. 2 (1.145) 252 45 146 77 158 100 163 89. t Teta solglium pyro- 15.0 0.0 38. 3 1.308 500 None 250 None 300 None 320 94. 2

p csp ate. do 20. 0 0. c 38, 3 1. 308 500 None 250 None 300 None 340 se f, Sodium metaphos- 2. 7 0.0 30. 2 1. 228 371 None 200 None 210 N one 210 91. 6

p ate. Dama #11 -7. 0 2. 8 29. 3 1.220 357 40 212 170 233 210 240 sc, o -Daxad #23..." 5. 6 2. 8 29. 3 l. 220 357 9() 230 170 230 210 250 100 Black liquor.. 8. 14 2.8 29. 3 1. 220 357 80 210 170 246 210 250 lUO Goulac 10.8 3. 2i 30. 2 1. 228 371 None 175 None 195 None 200 100 Glutrin soln.) 27. 0 2. 7 30. 2 1. 228 371 None 165 None 190 None 190 100 Trisodium phosphate. 26. 6 2. 65 31. 2 l. 238 (380) 45 170 85 200 142 220 lil4 (l 1 By weight.

-1In1000cc.oifeedpu1 3 Volume of solids afteiPl mim/volume of solids after 15 min. (both measured on the treated pulp).

Parentheses indicate calculated values. From the foregoing illustrative sedimentation curves it will be observed that my process has at r settling tank long enough to catch it; and it permits the recovery by sedimentation of ne material, by treatment with my newly-discovered acceleration reagents, even under conditions where no material at all would be recovered by sedimentation, within .the observed periods, as shownon the accompanying curves.

It is to be understood, also, that my invention is not primarily directed to any selective separation or concentration'of phosphate or phosphate ingredients per se; on the contrary, it is a method of producing an accelerated settling of fine particles of phosphate materials together with silica and other impurities. It permits the rapid` settling and recovery of solids in the pulp which would otherwise be lost, but without substantial -within the period of observation, in that instance amounting to sixteen minutes. That is to say, my novel reagents may produce settling of as much as 200 ccrof sedimented material per liter of treated pulp within the rst minute after treatment.

When the material is treated, of course, it should be permitted to remain in the settling tank for a unit of time suflicient to produce a substantial settling of the intermixed ne par- `.icles, after which the settled material is recovered from the tank and may thereafter be sub- .lected to a suitable process of selective separation, to separate the -valuable phosphate material from the impurities.

A suitable apparatus in which to carry out my cular one, about 100 feet in diameter. The susof Y line ore (which is a slurry collected pension plant) is pumped to from preceding parts of the 'the tank through a pipe or ilume discharging in a downward direction at the center of the tank. From that point the pulp flows radially outward in all directions, in the form of a thin sheet, fifty feet in radius. The overflow around the circumferential lip or edge of the tank is a matter of inches or less in depth, depending upon the rate of pumping and ilow of water, being ingeneral of the order of about an inch or less in depth. Below the lip, the tankis cylindrical for a distance oi about f our feet and then has a bottom in the general form of a very ilat inverted cone. The settled material collects on the bottom and is raked mechanically toward the discharge pipe at the apex of the cone. Thus the settling zone is about an inch, or less, in depth at the periphery, with a radiusof ilfty feet; and the particles need only settle through the depth of that zone. in order to fall below the lip of the tank, during the time required for the pulp to pass from the center to the rimof the tank. That time varies, of course, with different conditions, and is somewhat dicult to determine precisely. Calculation indicates an average time,lv

for this particular .illustrative installation, of around half a minute under certain conditions; less than two minutes in other cases, and a minutc vor less in still others, all depending on the rate of flow, the particular path of any given particle, and otherfactors. Once the particle settles sumciently below the level of the rim of the tank sov that; it is 'not carried over by the overflowing water, it is caught,V and can then settle at the bottom and be removed with` the settled product. The sedimentation-acceleration reagents are preferably added in the feed to the tank, as in a mixing tank ahead or the feed pipe;

although they can be added to the tank itself at the point where the inilow occurs.

Many other forms of apparatus and installalll tion. are suitable for application of my invention;

but the foregoing is described simply as an example of one suitable form of apparatus.

It will be seen that my invention, atleast according to one of its features,vand when appliedto a process for increasing the useful recovery of valuable phosphate fines by a commercial phosphosphate ore, specically Florida pebble phosphate, is mined, without grinding, in a manner producing a mixture including both coarse and lilnely divided particles oi' both valuable phosphate material and undesired impurities, such finely divided particles oi both phosphate and impurities including many particles which are too tine to settle rapidly in water. provides anim- `phate washer and concentrating plant, wherein portant improvement which constitutes a true f process, in which the successive steps include rial from the impurities. Another somewhat more specific embodiment of my invention is in a 'process for increasing the useful recovery of valuable phosphates by a. commercial phosphate washer and concentration plant, usually operating on Florida rock, wherein the ore containing the phosphate rock is Khydraulically mined and the resulting slurry is then fed to a settling tank, with or without in-v termediate treatment such as screening and the like, and in which the slurry comprises pieces of phosphate rock (i. e., 'phosphate mineral) of widely varying size, intermixed withimpurities such as silica, sand and clay, but the material is of unconsolidated nature, so that it does not require any preliminary crushing or grinding, which is employed upon certain Russian phosphate ores. In this respect, the improvement may comprise the steps of treating the slurry, as fed to the settling tank, sind preferably while it is free from any added froth flotation reagent (which might interfere with my treatment) with a settling-acceleration reagent of the class described. A suitable example is an alkaline reagent comprising an alkaline sodiumsllicate in an amount, and having an approximate composition, equivalent to about one pound of caustic soda, and about two pounds of sodium silicate, per ton of dry solids in the feed pulp. This treatment is found substantially to increase the rate of settling and to increase the amount of solids settled out per unit of time of settling operation. Thus more phosphate bearing material in the form of settled sediment is made usefully available for further treatment, such as subsequent steps of concentration of the phosphate. The nal result is to give a higher yield of phosphate concentrates, and consequently a higher recovery of phosphaterom the ore.

In a somewhat broader aspect, my invention is embodied in 'a similar process for increasing the useful recovery of valuable phosphate iines from a commercial phosphate mining and treating plant, wherein the phosphate ore is mined (hydraulically or -by dry-mining) in a manner which produces a mixture including both coarse and nely divided particles of both valuable phossuspension. In this case, the improvement may g5 be said to reside in first forming a' suspension, in water, of such intermixed ilne materials; then feeding the suspension to a settling tank; .treating thesuspension (either in the tank or before l 'fed thereto) with one or more of the settling- Y acceleration reagents deilned above, and in an amount and concentration suillcient to produce rapid sedimentation throughout the initial settling period, as during the first minute, and, preferably,l to more than double the volume of settledmateriahasoomparcdwithmaterlalor pulp not so treated, at all times throughout an initial settling period, as throughout the first three minutes ofsettling time. Such increase in the rate of settling is, in general, of :the intermixed fine particles of both phosphate materials and impurities, as compared with their untreated tling or sedimentation treatment of the present invention, are in general such as to necessitate .the production of a pulp or slurry which is-free of large size material (e. g., pieces plus about 14 mesh) and which has a content of solid material (comprising phosphate pre, i. e., phosphate mineral and impurities) of less than 40 per cent by weight, of the pulp-indeed more usually less than 30% and very often of the order of 10 to 15%, i. e., not more than 20%. The Isolid material is so suspended that rapid, economical natural settling of it is impossible. Thus, in pulps of the sort tested in the foregoing examples, less than about 40% of the `\solid material settles (without my treatment) in one minute of s ettling time, or usually, even in two minutes or more. For concentration and recovery of phosphate values from solid material such as is contained in such pulps, it is ordinarily prerequisite, for eillciency and economy, either that .the material be dry or nearly dry, or at least that it be in a relatively thick pulp; for instance, practicai wet concentration with reagents (e. g., tabling or froth notation) of ore exemplified by the types containing Florida, phosphate rock or debris, has been found to require, usually, a pulp feed of more than 50% solids content and preferably in most cases at least about 60%, and processes such as electrostatic concentration ordinarily require a' dry feed of solid material. The great practical value of my process should therefore be manifest, particularly in achieving the recovery from pulps or slurrles of an unavoidably dilute character, of a great deal more phosphate ore material (for subsequent concentration or other treatment) than it has heretofore been commercially practical to obtain.

'Ihe processes and reagents herein described, and the particular illustrative examples given, are the best embodiments -of my present invention now known to me; llout it isto be understood that the invention is not4 necessarily or specifically limited thereto, but may, under proper conditions, be carried out in other ways, Without departure from its spirit, and within the scope of the following claims.

I claim:

1. In a process for improving the recovery of phosphate ore 4material for subsequent concentration of phosphate values therefrom that is in the form of an aqueous pulp comprising a suspension of intermixed phosphate mineral and impurities in divided form as a result of hydraulically mining phosphate ore rock and screening out the large pieces of phosphate rock, said pulp having a content of said phosphate minerals and impurities of iess'than forty per cent, and the saidV suspension of said phosphate minerals and impurities being such that the major part of said phosphate-mineral and impurities is not recoverable by natural settling within the first two minutes of settling time, the steps of feeding the pulp to a settling tank immediately after screening out the large pieces of phosphate rock and not later than the time the pulp is received in the settling tank accelerating the settling of phosphate mineral and impurities by producing and maintaining the pulp in an alkalin condition and adding a deilocculating or dispersing agent thereto` tol more than double the volume of settled material, as compared with material not so treated, at the end of one minute of settling time following the time at which the pulp is allowed to commence settling, allowing said treated pulp t0 remain in the settling tank for a relatively short period of time suicient to provide sut)- stantially accelerated settling of phosphate mineral and impurities within not more than substantially ten minutes immediately following the time the pulp is received in the settling tank, to thus provide a settled product which upon withdrawal from the tank represents a substantially increased recovery4 of the intermixed phosphate mineral and impurities as compared with settling of untreated material in substantially the same time, collecting the settled product from the settling tank and then for the rst time sub- Jecting the same toconcentration treatment for recovery of phosphate values therefrom.

2. A process according to claim l in which the added agent comprises an alkaline sodium silicate in an amount, andhaving an approximate composition, equivalent to at least one pound of caustic soda and about one and one-half pounds of sodium silicate per ton of dry solids in the pulp.

3. A process according to claim l in which the added agent comprises sodium silicate.

4. A process according to claim l in which the added agent comprises wood pulp waste liquor materials.

5. A process according to claim 1 in which the added agent comprises material of the class consisting of alkaline sodium phosphate and molecularly dehydrated alkali phosphates.

6. A process according to claim l wherein the concentration treatment of the resultant settled product is by wet methods of concentration to obtain a Wet-phosphate producthaving increased content of useful phosphate material.

7. A process according to claim 1 wherein the concentration of the settled product is by flotation in order to produce an increased recovery of phosphate values.

DONALD S. PI-IELPS.

- V CERTIFICATE 'CF CORRECTION. Patent No. 2,381,511. August 7,1915.

- DONALD s.4 PHELPS.

It i's hereby Certified that error appears in tbe printed specification of the above mxmbered patent requiring correction es follows: Page 1]., -secvond column, line 5h, for re-pulsing read--re-pulpi'ng--q page second v coiumn, line Z., claim 1, strike out thevperiod after "to" first occurrence and "insert instead a Comma; and thatthe said Letters Patent shouldbe reed v with this correction therein that the same may conform to the record ofthe case -in the Patent Office. 4

Signed and sealed this 25th day' o.'` December, A. D. 1914.5.

Leslie Fralzer (Seal) First Assistant Cdnmissioner of. Patents. 

